I went through all of kf6 rpms and looked for the qt designer plugins and compared with Debian.

https://packages.debian.org/sid/amd64/libkf5itemviews-dev/filelist

has the Qt designer plugins in the -dev package.

We currently have two in the -devel packages:
https://src.fedoraproject.org/rpms/kf6-kxmlgui/blob/rawhide/f/kf6-kxmlgui.spec <-- in -devel
https://src.fedoraproject.org/rpms/kf6-knewstuff/blob/rawhide/f/kf6-knewstuff.spec <-- in -devel

The other ones I switched them over to the devel rpms with the following PRs:

https://src.fedoraproject.org/rpms/kf6-kitemviews/pull-request/2
https://src.fedoraproject.org/rpms/kf6-kplotting/pull-request/2
https://src.fedoraproject.org/rpms/kf6-kwidgetsaddons/pull-request/2
https://src.fedoraproject.org/rpms/kf6-kcompletion/pull-request/2
https://src.fedoraproject.org/rpms/kf6-kconfigwidgets/pull-request/2
https://src.fedoraproject.org/rpms/kf6-kiconthemes/pull-request/2
https://src.fedoraproject.org/rpms/kf6-ktextwidgets/pull-request/2
https://src.fedoraproject.org/rpms/kf6-kio/pull-request/2

In
https://src.fedoraproject.org/rpms/kf6-sonnet/pull-request/2

I added that to the outstanding PR

KDE PIM qt designer plugins:
https://src.fedoraproject.org/rpms/ktextaddons/pull-request/1
https://src.fedoraproject.org/rpms/akonadi-server/pull-request/3
https://src.fedoraproject.org/rpms/mailcommon/pull-request/3
https://src.fedoraproject.org/rpms/pimcommon/pull-request/3

Phonon:
https://src.fedoraproject.org/rpms/phonon/pull-request/2

Qwt:
https://src.fedoraproject.org/rpms/qwt/pull-request/5

Okteta (kf5 based)
https://src.fedoraproject.org/rpms/okteta/pull-request/5

KF5:
https://src.fedoraproject.org/rpms/kf5-kio/pull-request/8
https://src.fedoraproject.org/rpms/kf5-ktextwidgets/pull-request/1
https://src.fedoraproject.org/rpms/kf5-kconfigwidgets/pull-request/2
https://src.fedoraproject.org/rpms/kf5-kiconthemes/pull-request/1
https://src.fedoraproject.org/rpms/kf5-kcompletion/pull-request/1
https://src.fedoraproject.org/rpms/kf5-kitemviews/pull-request/1

Remove old docs stuff in kf5 from me and Rex:
https://src.fedoraproject.org/rpms/kf5-attica/pull-request/3
https://src.fedoraproject.org/rpms/kf5-kwidgetsaddons/pull-request/2
https://src.fedoraproject.org/rpms/kf5-kconfig/pull-request/4

All merged except
https://src.fedoraproject.org/rpms/pimcommon/pull-request/3

@thunderbirdtr thank you ;-)

https://src.fedoraproject.org/rpms/pimcommon/pull-request/3

merged by @aleasto Thank you :)

Issue closed. Thank you :)

@loise qscintilla still has its designer plugins in its main (not -devel) packages.